The dvdrom 163D that I killed in an accident, had a play and next button.. testing it out, it would only do all the work itself if I hit the buttons myself, otherwise everything would go through the OS.

So on a cd/dvdrom drive that has a volume and headphone jack, what is the point if there is no play button?

Is this why some manufacturers are removing those two things from the bezels?

the headphone jack is a monitor of the analog audio output. The volume is there, well, to control the volume. It's simply a convenience, particularly if you don't have an audio card, for those who want to play audio on the computer. Most systems auto-play audio CD's.